Magnetic field sensors have been commonly used in various electronic devices, such as computers, laptops, media players, smart phones, etc. There are several techniques/devices that can be used for detecting a magnetic field. Tunneling Magnetoresistance (TMR) is a promising magnetic sensing technology for handset applications due to its advantages in sensitivity, power, and process cost compared with other magnetic sensors. Another closely related technology in magnetic field sensing is Giant Magnetoresistance (GMR).
A TMR element is composed of two ferromagnetic layers separated by a non-magnetic, insulating tunnel barrier. One layer has a magnetization direction that is “free” to rotate in a magnetic field. The other layer has a “fixed,” reference magnetization that does not rotate when in a magnetic field of moderate to low strength that is of sensing interest. If the magnetization directions of the two layers are parallel to each other, the electrical resistance of the tunnel barrier is low. Conversely, when the magnetization directions are anti-parallel, the resistance is high. A magnetic field sensor based on TMR therefore converts magnetic field into electrical signal by a change in electrical resistance due to the changing angle of the magnetic free layer relative to the fixed layer in response to the field.
Typical magnetic sensors are restricted by the field range they can measure. Magnetic sensors have a sensitivity and measurement range built into the device by factors such as sense layer thickness, shape, and flux concentrator geometry. A magnetic sensor has good sensitivity and linear output corresponding to a certain magnetic field range. When the magnetic field is beyond the certain magnetic field range, the magnetic sensor may have nonlinear output and become less sensitive. On the other hand, a magnetic sensor with broader magnetic field measurement range may not have desired high sensitivity across the whole measurement range.
Therefore, it would be desirable to have a system, device, and method to effectively increase magnetic field measurement range of magnetic field sensors and maintain high measurement sensitivity.